1. Field of the Invention
The present invention relates to a polycrystalline silicon producing method, an apparatus for producing the polycrystalline silicon, and the polycrystalline silicon produced by the polycrystalline silicon producing method.
Priority is claimed on Japanese Patent Application No. 2009-167185, filed Jul. 15, 2009, the content of which is incorporated herein by reference.
2. Description of Related Art
As a polycrystalline silicon producing method, a method of producing by the Siemens method has been known. According to this polycrystalline silicon producing method, a plurality of silicon seed rods stand upright in a reactor and are supplied electric current and heated, and raw material gas including chlorosilane gas and hydrogen gas is supplied to the reactor to bring the raw material gas into contact with the heated silicon seed rods. On the surface of the heated silicon seed rods, polycrystalline silicon is deposited by heat decomposition or hydrogen reduction of the raw material gas and grows in a rod shape. In this case, every two silicon seed rods are paired and the upper end portions thereof are connected to each other by a connecting rod made of the same silicon as the silicon seed rod so that they are formed in an inverted (upside-down) U-shape or a Π-shape.
In the polycrystalline silicon producing method, there is a method of increasing an amount of raw material supply as one of methods of increasing a growth rate of polycrystalline silicon.
According to Japanese Unexamined Patent Application, First Publication No. 2003-128492, it is described that, when a supply amount of raw material gas is small, the deposition of polycrystalline silicon is insufficient, and by sufficiently supplying the raw material gas, a polycrystalline silicon growth rate increases. In addition, in Japanese Unexamined Patent Application, First Publication No. 2003-128492, it is described that an amount of raw material gas supply per square centimeter of a surface of a rod is controlled in the range of 3.5×10−4 to 9.0×10−4 mol/cm2min.
On the other hand, it is not preferable that raw material gas is excessively supplied because a ratio of the raw material gas contributing to the deposition reaction of polycrystalline silicon decreases, and thus a deposition amount of polycrystalline silicon per an amount of raw material supply (yield of the polycrystalline silicon) decreases.
Accordingly, it can be considered that by increasing an amount of raw material supply under the condition where the pressure in a reactor is increased, a growth rate is increased while the decrease of yield is suppressed. U.S. Pat. No. 4,179,530 describes that polycrystalline silicon is produced at a pressure of 1 to 16 bars, and preferably 4 to 8 bars. In addition, Published Japanese Translation No. 2007-526203 of the PCT International Publication describes that, although the Siemens method is not employed, deposition of polycrystalline silicon are achieved at a pressure of 1 millibar to 100 bar (absolute pressure).